Rotogravure printing of paperboard



April 1961 T. G. ZENTNER ETAL 2,980,015

ROTOGRAVURE PRINTING OF PAPERBOARD Filed June 6, 1956 f a. a E W r@ 0 ma z 5 Wm 1% V. W3 4 ROTOGRAVURE PRINTING F PAPERBOARD Thomas G. Zentner, Woodlawn, and Richard L. Boggs,

Middletown, Ohio, assignors, by mesne assignments, to

Diamond National Corporation, a corporation of Delaware Filed June 6, 1956, Ser. No. 589,818

I 3 Claims. (Cl. 101-170) Patent 0 duced when the in flow-out on the paper surface being printed occurs under or near the gravure roll and is so rapid and extensive as to form a film between the paper and gravure rollpsu rfaces which splits as the surfaces separate, thereby producing the pattern inherent in a film-splitting process. With the paper surface too ab- 1 sorbent, the split film of ink on it has insufficient time which are etched to form small depressions or cells-tdiffering as to area or depth orboth; The ink iwhich is to form the printed impression is contained within the cells or depressions, and when the continuous web is.

brought against the cylinder under heavy pressure from a rubber-surfaced impression roll the ink is transferred from the cells to the web. The ink is liquid, having for example a viscosity of 17 to 24 seconds at room temper'ature, 75 to 85 F., by the Number 2 Zahn cup method. The ink is applied to the cylinder so as to enter the cells or depressions, and then is wiped from'the outer cylinder surface so that it persists only in the depressions. t t

The intensity of the printed impression depends on the area and depth of thedepressionsr In areas where there are no depressions no printing will be done. If the depressions are large, deep andv closely spaced, a solid color impression may be made on the surface of the web.

to flow out into an even layer of liquid ink before it is absorbed; and therefore it reproduces on the paper surface the patterned appearance called worming or mottling.

Conversely, if the paper surface too strongly resists ink;

absorption, a solid color may be obtained by-flow-out in an area in which a half-tone effect was desired.

It, is an objectofthe invention to provide means and a method'for obviating or ameliorating the specific de fects outlined above.

It is an object of the invention to provide means and a method for the substantially automatic control and modification both of the surface compressibility of the web and of its absorptivity.

It is an objectof the invention to provide means and a method for producing a marked improvement in the;

rotogravure printing of continuous webs, particularly of paperboard, which will be cheap, convenient and capable of adequate control.

These and other objects of the invention which will be;

set forth hereinafter or will be apparent to one skilled in the. art upon reading these specifications, are ac-- complished by that construction and arrangement of parts and in that procedure of which an exemplary em bodiment will now be described Reference is made to the accompanying drawing, wherein: a V

Figure l is a diagrammatic side elevation of a portion of a rotogravure printing press. I

Figure 2 is a diagrammatic sectional view taken along I the line 22 of Figure l.

Smaller depressions apply inte'rspaced dots. of color tov the Web giving a half-tone effect.

Rotogravure presses are generally'large machines de-v signed to apply successive impressions in a plurality of colors. In presses for printing cartons thecylinders may be 20 to 40 inches or more in circumference and'more than 42 inches in length; and such presses may operateat lineal speeds up to several hundred feet per minute or more, for' example, 600, feet per minute.

After an ink impression has been made, that impression is dried as by passing the freshly printed web through a ventilated hot oven in which the air may be at a tern perature of 1.60 to 180 F., for examplerandthis is usuale; ly re'peatedafter each impression. jATfinal printing unit,

' is sometimes employed toapply a clear, over-print vvarnish 'to'the entire surface' of the web or to selected printed or unprinted areas of the surface." ,7 I 1 QA'number; of difiicul es have 'arisenIin the past "in; connection withthe continuous rotogravure printing "of uncoated and coated paperboard webspthe latter referring; to board withthe well known coating of, minera f lfi f fg and adhesive. Thedefectjof sriow'lfiakingi -occ'urswhere V V certain of thecellsforldepressions of the printing cylinder failf'tdmake a mark on theweb hyyielding their ink cbnteiit to'the Als'o ere "are conditions injtlie pri iets li a e r h eP s inkto'o' readily, on the-one;hand1tendipg" undesirably 'hol,carboxymethylcellulose, starch, protein, resin, and the H like. The uniformity of the application of the solution' was attributed primarilyto the rotogravurefprin'ting type- Briefly in the practice of the invention, it has been found that the application of moisture to the web in the way hereinafter set: forth will simultaneously affect thesurface compressibility of the web andtwill so unify and modify the abs'orptivity oftthe'web surface as to eliminate or ameliorate snow-flaking, worming and mottling, and produce a very great improvement in the overall printed impression;

Inour copending'application itis taught that a sub-I stantial improvement inrotogravure printing can be effected by using one'tof tlieprintirigstationsv to, apply to the webby rotogravure technique a water solution of an" a organic film" formingsubstance such as polyvinyl alcoof application; but it was also believed thatthe film formmg substance had an effect on uniformity. Thesba re application of the solution did not normally put the web I ,surface into the best condition for the reception Ofroto-t gravur'e printing; and it was the practice to'lpass' the, treated web through one of the drying ovens. in order to conditionjit for printing. The presence of'the film-' forming substance not onlyprevented too rapid loss of moisture in' the drying oven, but was relied uponth'ereafter to 'preservethe moisture content for use in'con trolling a plurality of printedrimpressions. The substitw I tionFof-plain water for the solution of film-forming substance was not found to be. satisfactory, for although .we- 'recognizedthat it was'possiblel the moisture, itself had' a primary efiect in controllingthe surface characteristics of the web water alone was notsufiiciently persistentin' the process to enable any improvement in printing to be noted."Moreover the use" of one of the printing staltions for the applicatioifof the controlsolu-tion cut dow' Patented Apr, 18, 1961 thetotal number of printed impressions'which could-beproduced in any given press.

We have now found that equivalent or superior results may be attained by the application of moisture in the absence of film-forming substances, in the wayherein-. after set forth, providing the moisture is applied in the form'of steam or vapor at a point so close to the pointtinuous web 1 passes beneath the unit under a pair of turning rolls 3 and 4, then travels upwardly, as at 1a, to a-turning roll 5. Thence it passes downwardly in a generally'diagonal direction, interrupted by its passage over turning rolls 6 and 7, to the printing means, which comprises a rubber coated pressure roll 8 and a rotogravure printing cylinder 9. The elements 8 and'9 coact toform the'printed impression on the web, the roll 8 serving to bring the web into contact with the cylinder 9. Means for inking the cylinder 9 and for wiping excess ink from its outer surface are diagrammatically indicated at 10 and require no description here.

Leaving the pressure roll 8, the web moves upwardly as at 1b passing over a turning roll 11, through a drying oven-Hand downwardly over a turning roll 13. The web may be thought ofas coming either from a supply roll or from a precedingsimilar unit of the press. After passing through the illustrated unit, the web may travel downwardly as at 10 either to a succeeding press unit or to a point at which it may be wound into a roll, out into sheets, or passed through cutting and scoring presses, if cartons are to bemade.

In; the practice of the invention steam may berapplied to; the surface of the web by means of a steam pipe 14, extending transversely of .the web and perforated at intervals with relatively small holes, closely spaced, which holes provide steamjets across that surface of the web whichis to receive the printed impression.

Referring to Figure 2, the pipe14 is connected to a source of steam through a conduit 15 which will contain a. control valve 16 and may advantageously be provided with a pressure gauge 17." The opposite end of the pipe 14 maybe closed if desired; but it is preferable to provide itjwith a depending condensate leg 13 having a valve 19 located above a condensate sump 20. Such an arrange-Q ment permits the formation of dry jets of steam without" the spraying of condensed water. The valve 19 is opened fully at-the beginning of an operation so that any water in thepipe 14 will be carried into the condensate leg and drained from the system. After the spray pipe has been heated up to the point where too little condensation occurs within the pipe to affect the dryness of the steam.

jets,,the valve 19 may be adjusted to a small opening such as will permit the removal of condensate only.

It .will be understood that the pipe 14 acts to treat the surface of the web uniformly with jets of live steam devoid of .waterpdrops or dropletsQso that the surface is,

treated with moisture of the form of vapor and hence is uniformly treated. The-application'of the moisture of.

the form of vapor should occur ahead of the printing station by a distance which, taking into account the speed of travel of the web and the moisture applied to it,rwill printing line.

travelingtportion of. the web. or into the nipof.tl1e.:,roll.!I..v

Where the jets are formed into the nip of a roll such as 5 or 7, they being of metal, corrosion may be obviated by chrome-plating the roll. The roll should not be so low in temperature as to produce condensation of the steam in droplets, which in turn transfers an uneven amount of moisture to the-web surface. However, there iscondensatio-n ofa thin film of moisture on the roll surface which prints onto the web surface evenly and which is. advantageous to preserve, even to the extent ofchilling theroll, as by cooling water. Moreover such roll chilling prevents undue heating of the web by the steam, as the process continues and heat from the steam accumulates.

It is impossible to state just how much moisture is added to the surface of the web, since the condition is so evanescent that measurements cannot be made. However, the factors involvedare readily controllable in the light of an examination of the printing being'accomplished. By way of a specific example, in a continuous multiple rotogravure press of the roll dimensions set forth above, the pipe 14 was a standard inch pipe having- 3 inch holes drilled along one side thereof at one inch spacings. Actual nozzle elements may be employed if desired. The pipe was located 3 inches from the surface ofthe web with the jets'directed into the nip of the roll 5. The pipe fittings in this instance were left loose enough so that the angle of steam application could beadjusted by slightly rotating the, pipe 14 by means of the condensate leg 19, with the pressoperating at normal speed (600 feet per minute).

In the particular press unit, the distance (tangential) between rolls 5 and 6 was 15 inches; the distance between rolls 6 and 7 was 3 inches; the distance between rolls 7 and 8 was ZOinches. A simple calculation using these values will show that the total distance traveled by the web at the specified normaloperating speed is such that the elapsed time between the application of the steam and the subsequent contact with the rotogravure cylinder is only about one third of one second. This distance was effect may be lost, just as, if the application is too close there may not' betime enough for the effect to take place.

However, the. specific distance is not critical, ,and can,

usually be determined, as'indicated, with reference to the construction of the printingunit.

Thus, after the system had attainedequilibriurn and, condensate was removed therefrom, the amount of moisture applied to the web in vapor forrn could beaccurate-f 1y adjustedbymeans of. the control'valve 16. Thisfadjustmentwas found easy-of accomplishment by observingthe quality of the printing being done; moreover itwas found readily possible to demonstrate the effect of the. applicationof moisture by turning :the valve 16 off at intervalsand noting the changeof the quality inthe,

printing. Afteneach suchdiscontinuance of steaming it'lwasiound that asfew minutes hadto be allowed for;

the system to reach equilibrium U Theeffect ofthe Steaming. is uniform and constant, and inrnorma'l operation does not require readjustment.

. result 1n n suitablyconditioned surface on the web at the It hasbeen found preferable to form; the :steam jets; I

during the course of along run. The improvement inv printing no only involvessubstantial elimination of snow! flaking, worming and mottling, jbut aIso'a gen eralimprjoveinent in, the-printed. result which; it is believed, can

only be due to at controlfof the effective absorptivity of thes permits the production (ate: more perfect impression by well as its specific absorptivity to give optimum printing.

In many instances it has been found that the procedure permits acceptable printing by rotogravure on board surfaces which otherwise could not be acceptably printed, thus rendering unnecessary the upgrading of the board. It has been found further that the practice of the process on coated boards provides a distinct and noticeable improvement in printing.

The effect of any one application of moisture in conditioning the web surface is temporary and will not persist beyond a single printing stage. However, the apparatus used is so simple, and the control so easy, that it may be duplicated for several or all of the printing stages operated in the press. If the process is operated for less than all of the printing stages it is usually readily possible by eye to distinguish those impressions which have been formed under the conditions outlined in this application from those formed without the application of moisture, even though these impressions be superposed one on the other.

The apparatus has been illustrated and described herein in a simplified form and refinements are both possible and desirable. For example, each steam system may be provided with an automatic inlet valve arranged to interrupt the flow of steam when the press is stopped. Manual opening of the inlet valve, however, permits the pressman to start the press before the steam is applied. Steam traps may be substitued for the condensation legs of the steam systems. The steam pipes are preferably insulated to diminish condensation and to guard against the burning of operating personnel. The steam can be limited to the zone of application by installing suitable bafiles, which may also serve to carry condensate to the side of the press. Provision may be made, if desired,

. 6' for changing the width of the jet application with changes in the widths of webs being printed.

Other modifications may be made in the apparatus and procedure without departing from the spirit of the invention. The invention having been described in an exemplary embodiment, what is claimed as new and desired to be secured by Letters Patent is:

1. In a rotogravure printing process wherein a continuous paperboard web is advanced at high speed into printing contact with an inked rotogravure cylinder along a printing line, the improvement comprising the steps of applying a thin, uniform superficial layer of hot moisture to the surface to be printed of the advancing web at a position ahead of and so spaced from the printing line that only a fraction of one second elapses between the application of the moisture and the subsequent contact with the rotogravure cylinder, said layer of m'oisture being limited to said surface of the web and having the effect of momentarily increasing the surface absorptivity and compressibility of the Web for said fraction of one second, and controlling the application of said moisture in relation to the speed of the advancing web to maintain said momentary effect.

2. The process defined by claim 1 wherein the layer of hot moisture is applied by jetting dry live steam uniformly across the advancing web.

3. The process defined by claim 2 wherein the elapsed time between the application of the hot moisture derived from the steam and the subsequent contact with the rotogravure cylinder is sufliciently long to achieve the effect of momentarily increasing the surface absorptivity and the compressibility of the Web, but said elapsed time is not longer than about one third of one second.

References Cited in the file of this patent UNITED STATES PATENTS Corlett Sept. 12, 

